1. Field of the Invention
Embodiments of the present invention generally relate to substrate processing systems and chambers used to process semiconductor wafers, solar panels, and flat panel displays and, in particular, to depositing electrically conductive pasting material in a plasma processing chamber.
2. Description of the Related Art
To help ensure semiconductor device integrity and performance, a semiconductor substrate is often cleaned prior to depositing a film on the substrate to remove contaminants and native oxides which may reside on the substrate surface. Conventional preclean processes typically include a sputter etch process to remove the contaminants and expose the native oxides. The native oxides may then be removed by additional sputter etching and/or reactive etching which uses a reduction reaction.
During chip packaging, metal layers are used for connecting solder material to bond pads that are electrically connected to semiconductor devices. Generally, incoming wafers for under-bump metallization (UBM) processes consist of metal pads embedded in a polymer passivation layer, such as a polyimide layer. The metal pads, such as aluminum pads, must be cleaned prior to UBM to remove any native oxide, such as aluminum oxide, from the surface of the metal pads.
Conventional preclean chambers and processes often do not uniformly clean the surface of the every smaller features being fabricated on a substrate. Failure to properly clean these features may result in void formation or increased electrical resistance between the surface features. The native oxides and other contaminants which are present on the features may cause void formation by promoting the uneven distribution of material deposited on the substrate in a subsequent processing step, or by causing the corners of the features to grow, merge, and seal off before the feature is filled with material being deposited therein. Precleaning processes are especially desirable to uniformly etch and clean substrate surface for subsequent barrier layer or metal deposition processes.
Conventional processes for removing aluminum oxide may include various halogen sputtering processes. Although the sputtering processes alone may be effective at removing the native oxide, they may also undesirably remove portions of the underlying aluminum material and the passivation resulting in redeposition on various chamber components. Other processes may include utilizing various chemical compounds, such as boron trichloride to remove the native oxide from the aluminum pads. However, when boron trichloride is used, residual chloride molecules may remain on the aluminum pads which must then be removed in subsequent processes. For example, the aluminum pads may be fluorized to remove the chloride in combination with a subsequent hydrogen peroxide process to remove any residual fluoride molecules that may remain on the aluminum pads. The aforementioned process requires multiple processing steps which consume valuable time which may reduce the overall throughput for performing precleaning processes.
Therefore, there is a need in the art for a native oxide removal process which reduces sputtered material in the chamber and which improves the efficiency of precleaning processes.